Two men have been seriously injured during an incident on board a ship at Port Hedland.

The Australian Maritime Safety Authority (AMSA) said the crew members from the Happy Buccaneer were injured by a "load spreader" just before midday.

The vessel, registered in the Netherlands, was moored at the Roy Hill South West Creek Wharf.

The pair were taken to Hedland Health Campus with leg injuries, where they are in stable condition.

Two AMSA inspectors are investigating.

Maritime Union of Australia's North West organiser Kyle McGinn said union representatives had been briefed on the incident.

"As far as I'm aware, there's been a serious incident onboard a foreign-manned vessel that was alongside the Roy Hill wharf," he said.

"This is again another foreign labour incident in the Pilbara.

"There have multiple incidents over the last 12 months involving foreign seafarers.

"Hopefully these men are covered under the ITF [International Bargaining Forum] agreement, which gives them some workers rights and they can be covered into their recovery.

"Any incident onboard a vessel involving machinery of this sort generally ends in either a serious incident or a fatality."

Roy Hill has released a statement saying its emergency response and medical personnel had assisted the injured pair.

"We received a request for assistance and our team immediately responded to the incident, providing medical treatment to the injured people before they were transported to Port Hedland hospital for treatment," the statement said.

"Our thoughts are with the injured people, their families and work colleagues."